The invention relates in general to the use of radio frequency identification (RFID) tags. In particular, the inventions relate to identifying one or more RFID tags that are moving along with a moving RFID reader.
Radio frequency identification (RFID) tags are electronic devices that may be affixed to items whose presence is to be detected and/or monitored. RFID tags are classified based on standards defined by national and international standards bodies (e.g., EPCGlobal and ISO). Standard tag classes include Class 0, Class 1, and Class 1 Generation 2 (referred to herein as “Gen 2”). The presence of an RFID tag, and therefore the presence of the item to which the tag is affixed, may be checked and monitored wirelessly by an “RFID reader”, also known as a “reader-interrogator”, “interrogator”, or simply “reader.” Readers typically have one or more antennas for transmitting radio frequency signals to RFID tags and receiving responses from them. An RFID tag within range of a reader-transmitted signal responds with a signal including a unique identifier.
With the maturation of RFID technology, efficient communication between tags and readers has become a key enabler in supply chain management, especially in manufacturing, shipping, and retail industries, as well as in building security installations, healthcare facilities, libraries, airports, warehouses etc.
Unlike bar codes, which are read in a line of sight by a laser reader, RFID tags are read wirelessly and not necessarily in a line of sight. This is an advantage in situations where there are tags affixed to objects that can not be seen, such as boxes stacked in a warehouse. An RFID reader in proximity of the tags senses them regardless of whether or not they can be “seen”. Although this is an advantage in managing many types of packages and materials, it is a disadvantage in one respect. Because RFID tags are read wirelessly using radio signals, it is not easy to identify particular tags that are moving coherently (synchronously) with a reader. For example, a forklift operator carrying a reader with him moves a pallet of goods, marked by an RFID tag affixed to the pallet, in a warehouse from point A to point B. There are hundreds of pallets in the warehouse. It may be useful to know which pallet is being moved at that particular time. One way of accomplishing this type of task is to read all tags within range at a point in time. Later, after one or more tags has been moved, the universe of tags remaining is read. Those that produce a read the second time have not been moved and can be subtracted from the universe of tags previously read. Tags that did not read are presumed to have been moved. This process is not convenient for many object management situations.
What is needed is a way of easily and quickly determining which tags are being moved along with an RFID reader in contrast to those tags that are not being moved or are being moved other than along with the RFID reader.